First-ever quantum network uses two atoms and a photon

Posted by Kate Taylor

Physicists say that, for the first time, they've created an elementary quantum network based on interfaces between single atoms and photons.

The network consists of two nodes, each of which can send, receive and store information, communicating via a single photon traveling along a 60-meter fiberoptic cable.

"This approach to quantum networking is particularly promising because it provides a clear perspective for scalability," says professor Gerhard Rempe, director at the Max Planck Institute of Quantum Optics.

In the prototype, single rubidium atoms are embedded in optical cavities composed of two highly reflecting mirrors placed very close together. A photon entering the cavity is reflected between the mirrors several thousand times, enhancing the atom-photon interaction.

First, the team trapped the atom quasi-permanently in the cavity using fine-tuned laser beams. Next, they achieved controlled emission of single photons from the trapped atom, transferring the information encoded in a single photon to a second single photon after a certain storage time.

"We were able to prove that the quantum states can be transferred much better than possible with any classical network," says project leader Dr. Stephan Ritter.

The scientists also succeeded in generating quantum mechanical entanglement between the two nodes, connecting them so that their properties are strongly correlated, wherever they are - Einstein's 'spooky action at a distance'.

The polarization of the single photon emitted by atom A is entangled with the atomic quantum state; and, once the photon gets absorbed, the entanglement is transferred to atom B.

"We have realized the first prototype of a quantum network. We achieve reversible exchange of quantum information between the nodes. Furthermore, we can generate remote entanglement between the two nodes and keep it for about 100 microseconds, whereas the generation of the entanglement takes only about one microsecond," says Ritter.

"Entanglement of two systems separated by a large distance is a fascinating phenomenon in itself. However, it could also serve as a resource for the teleportation of quantum information. One day, this might not only make it possible to communicate quantum information over very large distances, but might enable an entire quantum internet."